A Contrast Energy Model for Relative Numerosity Discrimination S Raphael, M Morgan |
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Visual Perception Group, Max-Planck-Institute Neurological Research, Germany
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| It has been suggested that numerosity is an elementary quality of perception, similar to colour. The mechanism for relative numerosity discrimination has proved elusive, in part because of the inevitable correlations between number, overall pattern size, density and size of the elements, all of which affect discrimination thresholds when they are varied. Here we suggest that relative numerosity is a type of texture discrimination, and provide a model of relative numerosity discrimination which computes the energy in two spatial frequency-tuned bandpass filters against which data can be tested and compare its ability to that of human observers. To test the model we measured the ability of human observers to distinguish patterns differing in numerosity and blur using a temporal 2AFC design in which a standard stimulus containing 64 dots in an equally sized area but with irregular shape was presented on each trial along with a test stimulus containing either fewer or more dots. Like some human observers, this mechanism finds it harder to discriminate relative numerosity in two patterns with different degrees of blur, but it still outpaces the human. We propose energy discrimination as a benchmark model against which more complex models and new data can be tested. |
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